Directional current relay

ABSTRACT

A current direction indicator including control means for performing a predetermined operation in a poly-phase electrical power system independently of the magnitude of current flow in the polyphase system. A separate current direction indicating circuit is provided for each phase and includes a first circuit for producing a signal in response to a change in polarity of current in one of the phases of the system, a second circuit for producing a signal functionally related to the polarity of the voltage between two of the phases of the system and a third circuit which produces an output signal when both signals of the first and second circuits occur simultaneously. The control means operates in response to the output signal to initiate the predetermined operation in the system.

United States Patent Plichta June 27, 1972 s41 DIRECTIONAL CURRENT RELAYPrimary Examiner-Robert K. Schaefer l Assistant Examiner-Mlliam J. Smith[72] Inventor. Michael J. Pllchta, Milwaukee, WIS. Atmmey mchard CRuppin [73] Assignee: McGraw-Edison Company, Elgin, Ill.

57 ABSTRACT [22] Filed: Sept. 1, 1971 1 A current direction indicatorincluding control means for per- [21] Appl' 176,912 forming apredetermined operation in a poly-phase electrical power systemindependently of the magnitude of current flow 52 US. Cl. ..307 127, 317010. 1 i P!YP system A l emen} i [5 l] Int. Cl. ..H02h 3/18 mg Pmv'dedfor each Phase and Includes a first 58 Field oiSeiu-ch. ..307/127, 130,131, 126, 125, '9 Signal in 3 change 307/236. 317/1316 1 328/1 1 8 ofcurrent In one of the phases of the system, a second circuit forproducing a signal functionally related to the polarity of 56 f n ed thevoltage between two of the phases of the system and a 1 Re are ces Clthird circuit which produces an output signal when both UNITED STATESPATENTS signals of the first and second circuits occur simultaneously.The control means operates in response to the output signal to llitevemon IIIIIIIIIIIIIIIIIIIII g: nitiate the edetermined operation inthe system. uncan PM: PM: 8 c

GROUND 14 Claims, 8 Drawing Figures TRIP CIRCUIT TIMING.

CIRCUIT GROUND 0U TPUT PATEmEDJum I572 SHEET 30F 3 1c Vac e pN w JM gIIII IN iwi wi w a DIRECTIONAL CURRENT RELAY BACKGROUND OF THE INVENTIONThis invention relates to a current direction indicator for analternating current power system.

In loop distribution power systems, circuit breakers are generallyarranged, and relay control is provided so that a fault occurring in anypart of the loop may be sectionalized and the load beyond the fault maybe fed from the source or sources througha part of the loop connectedaround the fault. It is common in such loop systems to place a normallyopen reclosing circuit breaker at the assumed zero load center of theloop. When the relay circuitry of this tie reclosing circuit breakersenses a loss of voltage on either side of itself, it closes to providea feed path through the unfaulted portion of the loop to the portion ofthe loop between the fault and the tie reclosing circuit breaker. Thecircuit breaker closest to the fault between the tie recloser and thefault will then sense overcurrent in the reverse direction feeding thefault and open in response to the reverse power flow to the fault. Sinceshortly after occurrence of the fault, a circuit breaker on the sourceside of the fault opened, the fault is now isolated and the systembeyond the fault is being fed through the tie recloser. In order toaccomplish this type of seetionalizing, the relay circuitry of eachcircuit breaker must include a first directional relay'which isoperative in response only to a forward fault overcurrent to initiateopening of the circuit breaker and a second directional relay which isoperative in response only to a lower level of fault overcurrent in thereverse direction to initiate opening of the circuit breaker. This typesystem thus requires two directional relays for each circuit breaker andalso requires a considerable length of time to close first the tiereclosing circuit breaker and then trip the sectionalizing circuitbreaker closest to the fault on the tie reclosing circuit breaker sideof the fault.

It is accordingly a general object of the invention to provide a currentdirection indicating means which is responsive only to current directionin an alternating current power system and is independent of themagnitude of the current flow to perfonn a predetermined operation inthe system. The invention includes a first circuit for producing a firstsignal in response to the change in polarity of either the current orvoltage in a phase of the system, a second circuit for producing asecond signal when the other one of the current and voltage quantitieshas a predetermined polarity, and a third circuit which is responsive tothe first and second signals to produce an output signal. The outputsignal is applied to a control means and in response thereto the controlmeans perfonns or initiates a desired operation in the system such aschanging a circuit breaker operating circuit so that it will respond toa lower level of current in the system.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates a circuit breakerincorporating the current direction indicator of the instant invention;

FIG. 2 illustrates the preferred embodiment -of the invention;

FIGS. 3, 4, and 5 are vector diagrams illustratingphase relationships ofquantities utilized in the current direction indicator illustrated inFIGS. 1 and 2; and

FIGS. 6A, 6B, and 6C graphically illustrate the interrelation betweenthe signals generated by the current direction indicator shown in FIG.2.

PREFERRED EMBODIMENT OF THE INVENTION Referring generally to thedrawings, FIG. I shows a three phase circuit breaker incorporating apreferred embodiment of the instant invention and including circuitbreaker switch 2 for interrupting voltage and the flow of current in athree phase system ABC. The current breaker includes an operatingcircuit 4, a control circuit 6 and a current direction indicatingcircuit 8. The operating circuit 4 includes an overcurrent sensingcircuit 10, a timing circuit 12 and a trip circuit 14. The

current direction indicating circuit 8 includes phase current directionindicating means 16 and ground current direction indicating means 18.Where there are three phases, as in the present case, each phase has aseparate directional circuit 20, 22, and 24. A common phase outputcircuit 26 is provided for the three directional circuits 20, 22 and 24of means 16, and a separate ground output circuit 28 is provided fortheground current direction indicating means 18. The phase A directionalcircuit 20 is shown in FIG. 2 as including a voltage squaring circuit30, a phase current peaking circuit 32 and an AND gate circuit 34. Thecircuits 30 and 32 of any one of the directional circuits 20, 22 and 24may be uncoupled from their associated phase A, B or C, for example byremoval of the line connections of transformers T5 and T6, withoutaffecting the signals produced by the circuits 30 and 32 associated withthe remaining coupled phases or the protection provided to these latterphases.

In the preferred embodiment of the invention, .each of the phasedirectional circuits 20, 22 and 24 and the ground current directionalindicating means 18 is similar in construction and operation except forthe manner in which each is connected to the system ABC. Therefore, forthe sake of brevity, only directional circuit 20 is illustrated indetail and will be discussed. In the detailed discussion of the currentdirection indicating circuit-8, the normal current direction in thealternating current system ABC is utilized as the reference currentdirection and this current direction is also considered to be thepreferred and forward current direction. When the current flow is not inthe normal direction, it is considered to be in the reverse ornon-preferred direction.

Reference is now made to FIG. 3 which shows the vector relationshipsbetween the line current and line-to-line voltages in the system ABCwhen current flow is in the preferred or forward direction and assuminga balanced load and unity power factor. It can be seen that the currentI, in phase A lags the voltage V from phases B toC by When current flowin the system ABC is in the non-preferred or reverse direction, all ofthe current vectors I I5, and I will be reverse so that the current I Awill lead the voltage V by 90, as shown in FIG. 5. These vectorrelationships are employed by the current direction indicating circuit 8for initiating a predetermined operation in the electrical power systemABC. In the present discussion, this predetermined operation is themodifying of current fiow to the operating circuit 4 whereby the time atwhich trip circuit 14 operates is also changed or modified. Toward thisend, the directional circuit 20 generates a first signal representativeof current vector 1, and a second signal representative of the voltagevector V If these two signals have a predetermined relation such asoccurrence within a predetermined time period, a control function isinitiated. It may be noted that the occurrence of the two signals andthe initiation of the control function may be independent of themagnitude of the current in the system ABC.

The directional circuit 20 including the phase current peaking circuit32 is shown in detail in FIG. 2. The circuit 32 is coupled to phase A bya current transformer T, and a half wave rectifying circuit 36 throughdiodes D3 and D4 and to the positive bus conductor 38 and negative busconductor 40 by bias resistors R2 and R4. The collector of transistor O2is connected to the junction between resistor R6 and capacitor C2 whichtogether comprise an RC time delay circuit connected across theconductors 38 and 40. The collector of transistor Q2 and the junctionbetween resistor R6 and capacitor C2 are also connected to the anode ofa programmable unijunction transistor Q4. The cathode of transistor 04is connected to the negative bus 40-through a resistor R8 and the gateof transistor 04 is connected through a surge resistor R10 and a pulseshaping capacitor C4 to the base of an output transistor Q6. The gate oftransistor 04 is also connected through resistor R10 to a voltagedivider comprising resistors R12, R14 and a temperature compensatingdiode D6. The base of output transistor O6 is connected to the positivebus 38 through leakage resistor R16 and surge surpressing capacitor C6.A diode D7 is also connected between positive conductor 38 and the baseof transistor 06 to provide reverse biasing protection for transistorQ6. A load resistor R18 is connected between the collector of transistorQ6 and the negative of bus 40.

The input transistor Q2 is conductive when its base potential ispositive relative to the negative potential connected to its emitter.When the transistor 02 is conductive, the potential between thecapacitor C2 and resistor R6 and at the anode of resistor O4 ismaintained close to the negative potential of conductor 40 so thatcapacitor C2 will not charge and transistor Q4 will be non-conductive.The voltage at the terminal 42 of current transformer T6 will follow thealternating wave form of current 1,, in phase A. When the potential atterminal 42 is positive relative to the potential at 44, current frompositive bus 38 will not flow toward terminal 42 but instead will flowthrough diode D5 and resistor R4 to the negative bus 40 so that the baseof transistor 02 will have some potential value higher than thepotential of conductor 40. This results in forward biasing andconducting of transistor Q2. When the potential at terminal 42 due tothe current I is negative relative to the potential at terminal 44,current from positive bus 38 will flow through resistor R2 and throughdiodes D4 and D3 toward terminal 42. This results in the potential atthe base of transistor Q2 being hear the negative potential of conductor40 so that transistor Q2 will not conduct. When transistor O2 isnon-conductive, the capacitor C2 charges to a level near that ofpositive bus 38. When the potential on capacitor C2 and thus thepotential applied to the anode of transistor Q4 reaches a level whichexceeds the potential on the gate of transistor Q4 as set by the voltagedivider comprising resistors R12 and R14, transistor Q4 will conduct todischarge capacitor C2 through resistor R8. Also, when transistor Q4conducts a pulse is generated at the gate of transistor 04 which isapplied through capacitor C4 to the base of output transistor Q6. Thispulse turns output transistor 06 on for a short time so that a positivepulse E is produced on conductor 46 at the cathode of diode D9.

The voltage squaring circuit 30 is shown in detail in FIG. 2 andincludes a switching transistor Q8 having its base connected to apotential transformer T5 through a resistor R20. A diode D8 is connectedbetween the base and emitter of transistor Q8. The collector oftransistor Q8 is connected to the negative bus 50 through resistor R22and to the AND circuit 34 through conductor 48. When the junctionbetween the resistor R and transformer T5 goes negative relative to theemitter of transistor Q8, the latter turns on to connect conductor 48 tothe positive bus 38. On the other hand, when the junction betweentransformer D5 and resistor R20 swings positive, the transistor Q8 willbe reverse biased by the drop across diode D8 so that it will not beconductive and conductor 48 will go to the negative potential of bus 50due to the connection through R22. This produces the square wave form Eon conductor 48, as shown in FIG. 63.

Referring again to the current peaking circuit 32, the voltage pulse Eappearing on conductor 46 represents the change in sense of polarity ofthe current flowing in phase A, but as a result of the time delayintroduced by the capacitor C2, the voltage pulse I5. is delayed. Thevoltage pulse E is shown in FIG. 4 as lagging the current I 4 by l35,however, the amount of lag may be adjusted by utilizing a capacitor orresistor of a different size. The pulse E is not a phasor quantity andtherefor it is represented in FIG. 4 by a broken line to indicate whereit occurs in relation to the voltage V and the current 1,. The voltagepulse E is shown in FIG. 6A to lead the position it is shown in FIG. 4by 90 since E is generated as 1,, passes through its zero point and notwhen 1,, is at its peak value. Thus, the voltage pulse E occurs at atime when the square voltage wave E is zero as shown in FIGS. 6A and613.

If the current in phase A reverses and flows in the nonpreferreddirection, the current vector I leads the voltage V by 90, as seen inFIG. 5. The voltage pulse -E also lags the current I,, by 135 andtherefore also lags the voltage V as shown in FIG. 5. The voltage pulse45., is shown in FIG. 6C adjusted for its generation as -I,, passesthrough its zero point and occurs at a time when E has a positive value,i.e., is present on conductor 40. If the current -I in the reversedirection is a fault current in phase A, the voltage pulse nowdesignated E' is delayed an additional 60 as shown in FIG. 5 forexample. However, the pulse E' also occurs when voltage E has a positivevalue, as shown in FIGS. 68 and 6C. Thus, since the voltage pulses E the-E' represent the voltage pulses on conductor 46, it may be seen thatwhen current 1,, in phase A is in a forward direction the voltage pulseE will not occur simultaneously with or within a predetermined time ofthe voltage E but that the voltage pulses E and -E' will occur at thesame time as voltage E Referring again to FIG. 2, the AND gate circuit34 comprises diodes D9 and D10 both having their anodes connectedthrough a resistor R24 to the positive bus 38. The cathode of diode D9is connected to the conductor 46 and therefore receives the voltagepulse applied to conductor 46. The cathode of diode D10 is connected toconductor 48 and therefore receives the voltage on conductor 48. Theanodes of diodes D9 and D10 are also connected to the anode of inputdiode D11 in the phase output circuit 26. As those skilled in the artwill appreciate, there will be no output from the AND gate circuit 34through diode D11 unless both of the conductors 46 and 48 are connectedto the positive bus 38. In other words, in order for an output from ANDgate circuit 34, there must be a simultaneous output signal from thephase current peaking circuit 32 and the voltage squaring circuit 30 asshown by the voltage pulses -E or -E' and voltage E in FIGS. 6C and 6B.As stated hereinabove, this occurs when there is current in the reversedirection in phase A.

The phase output circuit 26 includes an amplifier circuit comprisingtransistors Q10 and Q12. The collector of transistor Q10 is connectedthrough resistor R26 to terminal 52 of capacitor C8, the other terminalof which is connected to the positive bus 38. The emitter of transistorQ10 is connected to the base of transistor Q12 and to the negative bus40 through resistor R28. The collector of transistor Q12 is con nectedto the collector of transistor Q10 and its emitter is connected to theground bus 40. The transistor Q14 has its base connected throughresistor R30 to terminal 52 and to the positive bus 38 through leakageresistor R32. The emitter of transistor Q14 is connected to the positivebus 38 through diode D11 and the collector of transistor Q14 isconnected through resistor R34 and the parallel combination of capacitorC10 and resistor R36 to the negative bus 40. The collector of transistorQ14 is also connected through resistor R34 and zener diode D12 to thebase of transistor Q16. In addition, a leakage resistor R38 connects thebase of transistor Q16 to negative bus 40. The collector of transistorQ16 is connected through the resistor R40 to the positive bus 38 and itsemitter is connected directly to the negative bus 40. An outputtransistor Q18 has its base connected through the diode D13 to thejunction between resistor R40 and the collector of transistor Q16 and tothe negative bus 40 through leakage resistor R42.

The operation of the phase output circuit 26 is as follows. Outputtransistor Q18 is normally conductive and is turned off only after asignal is received at the base of transistor Q10. When the relativelyshort pulse from the AND gate circuit 34 is received at the base oftransistor Q10, the pulse signal is amplified by the transistors Q10 andQ12. The amplified signal charges capacitor C8. When the charge oncapacitor C8 reaches a predetermined value, the transistor Q14 isforward biased and conducts to complete a circuit through resistor R34to the cathode of zener diode D12 and through capacitor C10 and resistorR36 to the negative bus 40. This signal is initially insufficient tobreak down zener diode D12, however, after a time delay determined bythe charging time of capacitor C10 through R34, the breakdown voltage ofzener diode D12 is reached and a conducting circuit is then completedthrough zener diode D12 and resistor R38 to the negative bus 40. Thevoltage on the base of transistor Q16 then rises to forward bias Q16 andit also conducts to complete a conducting circuit through resistor R40to the negative bus 40. Conducting of transistor Q16 shunts the base oftransistor Q18 which then turns off to thereby provide an output signalby interrupting the previously conductive circuitfrom the positive busconductor 54 in control circuit 6 to the negative bus 40.

The control circuit 6 is also shown in detail in FIG. 2 and is coupledto the alternating current system ABC by means of potential transformerT4 and rectifying bridge D14. The positive bus conductor 54 of controlcircuit 6 is also coupled to a source of D.C. power (not shown) throughdiode D which serves to isolate the rippling output of bridge D14 fromthe power source. A zener diode D16 connected between the positive bus54 and the negative bus 50 serves as a regulator for the output from thebridge D14. A capacitor C12 filters the output of the bridge D14 andalso serves as an energy storage source for the control circuit 6. Thebase of a transistor Q is connected between a leakage resistor R46 anddiode D17 and the series combination of resistor R46, diode D17, andbias resistor R44 are connected across the positive bus 54 and negativebus 50. A leakage resistor R48 is connected to the emitter of transistorQ20 and the base of 022. The transistors Q20 and Q22 function. as anamplifying circuit to provide an output signal through a relay coil 56.A discharge circuit through diode D18 for relay coil 56 is provided andFIG. 2 shows an operating connection from coil 56 which leads tocontacts 560- in FIG. 1.

The transistors Q20 and Q22 are normally off and in this condition, thecoil 56 is deenergized and the contacts 56a-f have their conditionsshown in FIG. 1. The transistors Q20 and Q22 are in their normal offcondition whenever the transistor Q18 in phase output circuit 26 isconducting or when a transistorcorresponding to Q18 is conducting in theground output circuit 28. A conductor 58 similar to conductor 60 isshown in FIG. 2 as leading to the ground output circuit 28. Theconductor 58 is connected within circuit 28 to the transistorcorresponding to Q18. When transistor Q18 is conductive, it provides aconductivecircuit from the positive bus 54, through resistor R44 anddiode D19 to the negative bus 40 to thereby shunt biasing current aroundthe base of transistor 020 so that transistor Q20 and thereforetransistor Q22 remain ofi. Only if both transistor Q18 and thecorresponding transistor in the ground output circuit 28 turn off willcurrent flow through resistor R44, diode D17 and resistor R46 to forwardbias Q20 and turn transistors Q20 and Q22 on. It may be appreciated thatseveral variations of the control circuit 6'are possible. For example,the transistor Q18 and the corresponding transistor in ground outputcircuit 28 may be separately and independently connected to a transistoramplifying circuit such as transistors Q20 and Q22 which wouldindependently provide different output signals to the coil 56. With sucha circuit arrangement, either an output signal from phase output circuit26 or an output signal from ground output circuit 28 would result in anoutput signal to relay coil 56. When an output signal is produced torelay coil 56, it switches the contacts 56a-f to their positionsopposite from those shown in FIG. 1. As will be seen hereinafter, thisswitching and thus the current direction relay of the present inventionchanges the overcurrent level at which a time delay can be completed topermit opening of circuit breaker switch 2.

The operating circuit 4, as shown in FIG. 1, includes a timing circuit12 and a trip circuit 14. The timing circuit 12 and trip circuit 14 areboth coupled to the alternating current system ABC through currenttransformers T1, T2 and T3 and full wave rectifying bridges D21, D22 andD23. Resistors R50, R52, and R54 respectively connected in parallel withthe bridge rectifiers D21, D22 and D23. Resistors R56, R58 and R60 arerespectively connected in parallel with resistors R50, R52 and R54through relay coil contacts 561:, 56d and 56f. In the normal conditionof contacts 56b, 56d and 56f as shown in FIG. 1, the resistors R56, R58,and R60 are effectively in circuit with resistors R50, R52, and R54.Resistors R62 and R64,

and R66 are respectively connected in series with bridge rectifiers D21,D22, and D23. Resistors R62, R64, and R66 are effectively out of circuitwith resistors R50, R52, and R54 when the contacts 560, 56c, and 56e arein their normally open conditions as shown in FIG. 1.

When the contacts 56a-f have the condition shown in FIG. 1, thesecondary current of the current transfonners T1-T3 will produce voltagedrops which are divided between the various resistors for each phase.For example, considering phase A, when contact 560 is open and contact56b is closed, resistors R50 and R56 will be effectively in parallel andresistor R62 will be effectively in series with the parallel combinationof R50 and R56. The voltage drop generated by the secondary current ofcurrent transformer T1 will divide between resistor R62 and the parallelcombination of R50 and R56. Because the effective resistance of parallelconnected resistors is less than the resistance of each one of theresistors alone, the voltage drop across the parallel combination of R50and R56 and therefore the voltage drop across capacitor C14 will belower than the voltage drop across R50 alone. Also because the resistorR62 takes a portion of the total voltage drop, the drop on R50 is lessthan when R62 is shunted by contact 56a. Accordingly, when contacts56a-f are in their conditions opposite from that shown in FIG. 1, thetotal voltage drop due to the secondary currents of transformers T1-3will respectively appear across resistors R50, R52 and R54. Each one ofthese voltage drops will be larger than when the contacts 56a-f are intheir condition shown in FIG. 1 for equal values of transformercurrents. Thus, modifying of the current flow paths through resistorssuch as R50, R56, and R62 to vary the voltage drop appearing capacitorC14 changes the time delay provided by timing circuit 12 as will bediscussed hereinafter. v

The timing circuit 12 functions with the overcurrent sensing circuit 10to provide a time delay which is inversely proportional to the magnitudeof the current flowing in one of the phases A, B, or C. Both the timingcircuit 12 and the trip circuit 14 are of types well known in the artand will be discussed only in general terms here. The capacitor C14serves as a means of controlling the timing circuit 12 in accord withthe current flowing in any of the phases, A, B, or C. The time delayprovided by timing circuit 12 is determined by the voltage dropappearing across capacitor Cl4 and therefore by the magnitude of currentflow in any one of the phases A, B, or C. At the end of the time delayprovided by timing circuit 12 a signal is applied to the trip circuit 14which, in turn, trips the main circuit breaker switch 2 so that it movesto its open position and interrupts conduction of phases A, B, and C. Aspreviously discussed, the voltage drop appearing across capacitor C14will be only a portion of the total voltage drop across the resistors ofovercurrent sensing circuit 10 when the contacts 56a-f are in theirconditions shown in FIG. 1. When the contacts 56a-f have theirconditions opposite from that shown in FIG. 1, the voltage drop incapacitor C14 will be substantially all of the total voltage drop acrossthe resistors of the overcurrent sensing circuit 10.

Thus, for equal values of current in the system ABC, the condition ofthe contacts 56a-f shown in FIG. 1 results in a relatively small voltagedrop across capacitor C14 and when the contacts a-f have a conditionopposite from that shown in FIG. 1 a larger voltage drop appears acrosscapacitor C14. Since this voltage drop controls the length of the timedelay provided by timing circuit 12, the time delay is in elTectcontrolled by the direction of the current in any one of the phases A,B, or C as indicated by the phase current direction indicating means 16or by the direction of ground current as in dicated by ground currentdirection indicating means 18.

To summarize, when fault current occurs in the forward or preferreddirection in phases A, B, or C voltage drop appears across one or moreof the low resistance parallel combinations of resistors R50, and R56,R52 and R58, and R54 and R60 and also across capacitor C14. Due to thefact that forward fault currents are usually of a high magnitude, thisvoltage drop will nevertheless be substantial. Therefore, due to theinverse proportionality characteristic of timing circuit 12, the timingcircuit 12 provides a relatively short time delay after which the tripcircuit 14 is actuated to trip the circuit breaker switch 2 to its openposition. In the event that current flow is in the non-preferred orreverse direction in any one of phases A, B, or C or in the groundconnection of these three phases, one of the directional circuits 20,22, 24 or ground current direction indicating means 18 will produce asignal indicative of the reverse flow direction of current. Usingdirectional circuit 20 as being illustrative, this is accomplished bythe simultaneous generation of a signal from voltage squaring circuit 30and phase current peaking circuit 32 to AND circuit 34 which in turnproduces a third signal to the phase output circuit 26. When the outputtransistor Q18 of phase output circuit 26 turns off and thecorresponding output transistor of ground output circuit 28 also turnsoff, the control circuit 6 energizes its relay 56 which switches thecontacts a-f to their conditions opposite from that shown in FIG. 1. Thevoltage drop then ap' pearing across the capacitor C14 due to currentflow in the non-preferred direction will still be substantial since onlyR50 is in parallel with C14, even though reverse fault current may be ofa lower magnitude than forward fault current. Again, after the inverselyproportional time delay of timing circuit 12, the circuit breaker switch2 will be tripped open. Similarly, if the reverse overcurrent is of ahigh magnitude the time delay will be faster than either the usualreverse current time delay or the forward overcurrent time delay.

It is thus seen that a combined current direction indicating circuit andcontrol circuit have been provided for modifying the time delay prior tointerrupting of the alternating system ABC independently of themagnitude of current flow in the system ABC. Although the modificationhas been accomplished by changing the overcurrent sensing portion of thecircuit operating circuit, the modification may also be accomplished bychanging the timing capacitor arrangement normally included in timedelay circuits such as illustrated herein.

Moreover, the disclosed current direction indicating means and controlmeans may be utilized to perform other functions in the system ABC notinvolving the level of current flow in the system. Some of these includeblocking of instantaneous trip of the circuit breaker switch, preventingreclosing of the circuit breaker switch after it opens, and indicatingfunctions such as providing an alarm to a remotely located dispatchpoint.

It will also be appreciated by those skilled in the art that the currentpeaking circuit 32 and voltage squaring circuit 30 can be reversedrelative tothe system voltage and current so that current squaring andvoltage peaking circuits are provided. Also, while the invention hasbeen illustrated and described in relation to a poly-phase system, itcould also be employed with a single phase system wherein only a singledirectional circuit would be employed.

Accordingly, while only a single embodiment of the instant invention hasbeen shown and described, the scope of the invention is not to belimited to the disclosed specific embodiment.

I claim:

1. In an electrical power system for producing alternating polarityvoltage and current quantities, the combination comprising:

circuit means for performing a predetermined operation in saidelectrical power system;

control means coupled to said circuit means and operative independentlyof the magnitude of said current and voltage quantities for controllingsaid operating circuit means; and

a current direction indicator including:

first circuit means coupled to said system for producing a first signalin response to the change in polarity of one of said quantities;

second circuit means coupled to said system for producing a secondsignal when the other one of said quantities has a predeterminedpolarity; and

third circuit means coupled to said first circuit means,

said second circuit means and said control means and being responsivetoe the occurrence of both of said signals during a predetermined timeperiod to produce a third signal to the control means whereby the latteris actuated to control the operating circuit means.

2. The combination according to claim 1 wherein said control meanscomprises circuit means for modifying current flow to the operatingcircuit means.

3. The combination according to claim 2 wherein said operating circuitmeans comprise current level sensing means coupled to said control meansand being responsive to said current flow for initiating interruption ofthe voltage and current quantities in said system, said level sensingmeans being operative after a time delay inversely proportional to thelevel of said current flow whereby said control means controls said timedelay as a function of the current direction in said system.

4. The combination according to claim 1 wherein:

said first circuit means includes a phase current circuit coupled tosaid system and producing said first signal in response to change inpolarity of a phase current in said system, said first circuit meansalso including a ground current circuit coupled to said system andproducing said first signal in response to change in polarity of groundcurrent in said system;

said second circuit means includes a phase-to-phase voltage circuitcoupled to said system and producing said second signal when aphase-to-phase voltage in said system has said predetermined polarity,said second circuit means also including a phase-to-neutral voltagecircuit coupled to said system and producing said second signal when thephase-to-neutral voltage has said predetermined polarity; said thirdcircuit means includes output circuit means connected to said controlmeans, said output circuit means producing said third signal in responseto the occurrence during said predetennined time period of the first andsecond signals respectively from the phase current circuit and thephase-to-phase voltage circuit or in response to the occurrence duringsaid predetermined time period of the first and second signalsrespectively from the ground current circuit and the phase-tomeutralvoltage circuit.

5. In an electrical power system producing alternating polarity voltageand current quantities, a current direction indicator comprising:

first circuit means coupled to said system and including a relaxationoscillator circuit for producing a first signal in response to a changein polarity of one of said quantities; second circuit means coupled tosaid system for producing a second signal when the other one of saidquantities has a predetermined polarity; and third circuit means coupledto said first circuit means and said second circuit means and beingresponsive to the occurrence of both of said signals during apredetermined time period to produce a third signal indicative ofcurrent flow in said system in a predetermined direction.

6. The combination according to claim 5 wherein said first circuit meansincludes a current transformer coupled to said system and having asecondary winding producing an alternating polarity current to saidrelaxation oscillator circuit, the operation of said relaxationoscillator circuit being inhibited while said transformer current has apredetermined polarity.

7. The combination according to claim 6 wherein said relaxationoscillator circuit produces a fourth signal and comprises a threeelectrode static switch including an anode receiving said fourth signal,said static switch being conductive in response to receipt of the fourthsignal at said anode.

8. The combination according to claim 6 further comprising control meanscoupled to the third circuit means and being operative independently ofthe magnitude of said current quantity for performing a predeterminedmodification to said electrical power system in response to said thirdsignal.

9. The combination according to claim 7 further compristime delay meanshaving a controllable variable time delay period for delayinginterruption of said electrical power system; and wherein said controlmeans is operative to control said variable time delay period.

10. In an electrical power system producing an alternating polarityvoltage quantity, a current quantity flowing in either of two oppositedirections, and including a circuit breaker for interrupting saidsystem, the combination comprising;

circuit breaker operating means including time delay circuit means fordelaying operation of the circuit breaker, said time delay circuit meanshaving two different conditions each corresponding to one of theopposite flow directions of the current quantity and having a variabletime delay determined by said conditions;

first circuit means coupled to said system for producing a first signalin response to a change in polarity of one of said quantities;

second circuit means coupled to said system for producing a secondsignal when the other one of said quantities has a predeterminedpolarity; and

third circuit means for sensing the occurrence of said first and secondsignals within a predetennined time period, the occurrence of saidsignals within said time period indicating a flow of said currentquantity in one of said opposite directions, said third circuit meansbeing responsive to the occurrence of said signals within saidpredetermined time period to operate the time delay circuit means fromone of said conditions to the other of the conditions whereby said timedelay period is varied.

11. The combination according to claim 10 wherein the third circuitmeans is responsive to the simultaneous occurrence of said first andsecond signals to operate the time delay circuit means from one of saidconditions to the other.

12. The combination according to claim 10 wherein:

said circuit breaker operating means includes a current first circuitmeans includes:

a current transformer coupled to said system and having a secondary coilproducing an alternating polarity current; and

a relaxation oscillator circuit coupled to said secondary coil andoperative signal in response to the alternating current from thesecondary coil.

14. The combination according to claim 10 wherein:

said electrical power system comprises a three phase system;

said first circuit means produces a first signal for each one of saidphases;

said second circuit means produces a second signal for each one of saidphases;

said third circuit means is responsive to the occurrence of said firstand second signals related to the same one of any of said three phaseswithin said predetennined time period to operate the time delay circuitmeans from one of said conditions to the other of the conditions; and

the coupling of said first and second circuit means to said three phasesis removable from the same one of any of said phases, said first andsecond circuit means producing the first and second signals related tothe remaining coupled phases to the third circuit means independently ofthe removal of the coupling of the first and second circuit means to theone phase.

i I #l i i

1. In an electrical power system for producing alternating polarityvoltage and current quantities, the combination comprising: circuitmeans for performing a predetermined operation in said electrical powersystem; control means coupled to said circuiT means and operativeindependently of the magnitude of said current and voltage quantitiesfor controlling said operating circuit means; and a current directionindicator including: first circuit means coupled to said system forproducing a first signal in response to the change in polarity of one ofsaid quantities; second circuit means coupled to said system forproducing a second signal when the other one of said quantities has apredetermined polarity; and third circuit means coupled to said firstcircuit means, said second circuit means and said control means andbeing responsive toe the occurrence of both of said signals during apredetermined time period to produce a third signal to the control meanswhereby the latter is actuated to control the operating circuit means.2. The combination according to claim 1 wherein said control meanscomprises circuit means for modifying current flow to the operatingcircuit means.
 3. The combination according to claim 2 wherein saidoperating circuit means comprise current level sensing means coupled tosaid control means and being responsive to said current flow forinitiating interruption of the voltage and current quantities in saidsystem, said level sensing means being operative after a time delayinversely proportional to the level of said current flow whereby saidcontrol means controls said time delay as a function of the currentdirection in said system.
 4. The combination according to claim 1wherein: said first circuit means includes a phase current circuitcoupled to said system and producing said first signal in response tochange in polarity of a phase current in said system, said first circuitmeans also including a ground current circuit coupled to said system andproducing said first signal in response to change in polarity of groundcurrent in said system; said second circuit means includes aphase-to-phase voltage circuit coupled to said system and producing saidsecond signal when a phase-to-phase voltage in said system has saidpredetermined polarity, said second circuit means also including aphase-to-neutral voltage circuit coupled to said system and producingsaid second signal when the phase-to-neutral voltage has saidpredetermined polarity; said third circuit means includes output circuitmeans connected to said control means, said output circuit meansproducing said third signal in response to the occurrence during saidpredetermined time period of the first and second signals respectivelyfrom the phase current circuit and the phase-to-phase voltage circuit orin response to the occurrence during said predetermined time period ofthe first and second signals respectively from the ground currentcircuit and the phase-to-neutral voltage circuit.
 5. In an electricalpower system producing alternating polarity voltage and currentquantities, a current direction indicator comprising: first circuitmeans coupled to said system and including a relaxation oscillatorcircuit for producing a first signal in response to a change in polarityof one of said quantities; second circuit means coupled to said systemfor producing a second signal when the other one of said quantities hasa predetermined polarity; and third circuit means coupled to said firstcircuit means and said second circuit means and being responsive to theoccurrence of both of said signals during a predetermined time period toproduce a third signal indicative of current flow in said system in apredetermined direction.
 6. The combination according to claim 5 whereinsaid first circuit means includes a current transformer coupled to saidsystem and having a secondary winding producing an alternating polaritycurrent to said relaxation oscillator circuit, the operation of saidrelaxation oscillator circuit being inhibited while said transformercurrent has a predetermined polarity.
 7. The combination according toclaim 6 wherein said relaxation oscillator circuit produces a fourthsignal and comprises a three electrode static switch including an anodereceiving said fourth signal, said static switch being conductive inresponse to receipt of the fourth signal at said anode.
 8. Thecombination according to claim 6 further comprising control meanscoupled to the third circuit means and being operative independently ofthe magnitude of said current quantity for performing a predeterminedmodification to said electrical power system in response to said thirdsignal.
 9. The combination according to claim 7 further comprising: timedelay means having a controllable variable time delay period fordelaying interruption of said electrical power system; and wherein saidcontrol means is operative to control said variable time delay period.10. In an electrical power system producing an alternating polarityvoltage quantity, a current quantity flowing in either of two oppositedirections, and including a circuit breaker for interrupting saidsystem, the combination comprising; circuit breaker operating meansincluding time delay circuit means for delaying operation of the circuitbreaker, said time delay circuit means having two different conditionseach corresponding to one of the opposite flow directions of the currentquantity and having a variable time delay determined by said conditions;first circuit means coupled to said system for producing a first signalin response to a change in polarity of one of said quantities; secondcircuit means coupled to said system for producing a second signal whenthe other one of said quantities has a predetermined polarity; and thirdcircuit means for sensing the occurrence of said first and secondsignals within a predetermined time period, the occurrence of saidsignals within said time period indicating a flow of said currentquantity in one of said opposite directions, said third circuit meansbeing responsive to the occurrence of said signals within saidpredetermined time period to operate the time delay circuit means fromone of said conditions to the other of the conditions whereby said timedelay period is varied.
 11. The combination according to claim 10wherein the third circuit means is responsive to the simultaneousoccurrence of said first and second signals to operate the time delaycircuit means from one of said conditions to the other.
 12. Thecombination according to claim 10 wherein: said circuit breakeroperating means includes a current transformer coupled to said systemand having a secondary winding producing current proportional to thecurrent in said system; the time delay of said time delay circuit meansis inversely proportional to the magnitude of said secondary windingcurrent, and the time delay circuit means has a different magnitude ofsecondary current flowing in it in each of said different conditions.13. The combination according to claim 11 wherein said first circuitmeans includes: a current transformer coupled to said system and havinga secondary coil producing an alternating polarity current; and arelaxation oscillator circuit coupled to said secondary coil andoperative signal in response to the alternating current from thesecondary coil.
 14. The combination according to claim 10 wherein: saidelectrical power system comprises a three phase system; said firstcircuit means produces a first signal for each one of said phases; saidsecond circuit means produces a second signal for each one of saidphases; said third circuit means is responsive to the occurrence of saidfirst and second signals related to the same one of any of said threephases within said predetermined time period to operate the time delaycircuit means from one of said conditions to the other of theconditions; and the coupling of said first and second circuit means tosaid three phases is removable from the same one of any of said phases,said first and second circuit means producing the first aNd secondsignals related to the remaining coupled phases to the third circuitmeans independently of the removal of the coupling of the first andsecond circuit means to the one phase.